Process of making cast tool steel



Patented Apr. 2, 1940 PROCESS OF MAKING CAST TOOL STEEL Charles Baird,Detroit, Mich.

No Drawing.

16 Claims.

This invention relates to processes for preparing cast tool steelcapable of being directly used for cutting tools such as tool bitswithout forging or metal working operations.

More specifically the invention relates to the production of cast highspeed steel tool bits without forging or hot working the metal andwithout heating the bits above the critical temperature of the highspeed steel by melting a high speed steel in an indirect are electricfurnace, casting the molten metal in molds of the approximate tool sizeand grinding the castings to shape.

Metal cutting tool steels have a definite range of carbide particle sizeand grain size for best performance in a certain class of operation. Ifthe carbide particles and grains of the metal have sizes that are toosmall, the tool will fail too rapidly at the cutting point as a resultof the high temperatures combined with the abrasiveness of the metalmachined. It is thus obvious that cutting steels with too small grainand carbide particle sizes are commercially inferior in certainoperations to those having the larger sizes.

If the) grain and carbide particle sizes of the cutting steel are toolarge tobe within the definite range of carbide and grain particle sizesfor cutting steel, the cutting tool will be too brittle, both at itscutting point or edge and at its holding or gripping end, for commercialuse.

It has been the practice, in making cuttin tools, to cast high speedsteels with a grain and carbide particle size too large to be includedwithin the desired range for cutting tools. The cast steel has then beenhot worked or forged to the desired grain size. This process, of course,is expensive and the hot working operations have some deleterious effectupon the steel.

The Langenberg U. S. Patent 1,492,567 discloses a process of making toolsteels without forging or hot working the metal by melting a high speedsteel, high in molybdenum content, in an electric or crucible furnace.The molten metal is cast in molds to the approximate desired tool sizeand the castings are then heated to temperatures from 900 to 1050 C.,(1652 to 1922 F.) which temperatures are above the critical temperatureof the steel. The castings are cooled and reheated to between 725 C. to850 C. (133'7 to 1562 F.) until the molybdenum carbides are uniformlydistributed throughout the mass. The castings are then ground to shapeand given the usual heat treating cycle for high speed steels includinganother heating to above the critical point of the steel.

. quenched to room temperatures.

Application December 10, 1937, Serial No. 119,107

I have now found that the melting of a ferrous tool steel charge in anindirect arc rocking electric furnace has a. definite effect upon thegrain and carbide particle size of the metal. Castings of high speedsteel poured from the indirect are electric furnace have grain andcarbide particle sizes within the range desired for cutting tools. Ifthese castings are of the approximate tool size, the same need only beground for direct use as cutting tools.

My process therefore not only avoids the heretofore necessary hotworking, or forging operations but also renders unnecessary the heattreatment of high speed steels above their critical temperature.

The ferrous metal cast tool steels of this invention have longer toollife than the best heretofore known ferrous metal tools of similarcomposition.

I have also discovered that the cutting ability and resistance to impactof some ferrous metal high speed tool steels, such as steels of the18-4-1 type, prepared according to this invention can be increased bysubjecting the tools to a single or to a double draw heat treatment attemperatures below the critical temperature of the steel.

The single draw heat treatment comprises a heating of the castings totemperatures of from 1000 to 1150 F., for a period dependent upon themass of castings, followed by a cooling in circulating air to roomtemperature. A heat treatment at 1000 to 1150 F. for thirty minutes toone hour is usually sufficient for tool bits. Thus a tool bit 8-10" inlength and A square need only be heated for one hour. If temperaturesabove 1150 F., but below the critical temperature of the steel, are usedin the heat treatment, the time may be decreased. Thus a heat treatmentat 1650 F. for ten minutes might be sufflcient.

The double draw heat treatment includes heating the castings totemperatures around 1050" F. for a period dependent upon the mass of thecastings as explained above, cooling the heated castings suflicientlyslow to prevent formation of cracks and reheating the cooled metal totemperatures around 1050 F. The reheated metal is then eitherrapidly oilquenched or slowly air Cooling from the first heat treatment ispreferably effected in circulating air since-this treatment issuficiently slow to prevent the formation of cracks.

Ferrous metal high speed steel alloys with an iron content of from 15%to 85%, a carbon con- I tent of from 0.6%to 2%, and the balance selectedfrom the group comprising tungsten,

molybdenum, chromium, vanadium and cobalt are useful materials for theprocess of this invention. The steel alloys may also contain minoramounts of nickel and tantalum or other secondaryalloys. Steel alloyshaving a high iron content of from 60% to 80% and the balance one ormore of the following elements: tungsten, molybdenum, chromium, vanadiumand cobalt, are desired alloys for the process of this invention.

Specifically, high speed steel alloys of the 18-4-1 type (18% tungsten,4% chromium, 1% vanadium, balance iron) are preferred for the process ofthis invention.

It is then an object of this invention to provide high speed toolswlthoutforging or hot working operations, and without heat treating themetal above its critical temperature.

Another object of this invention is to provide cast tool steels fromhigh speed steels without hot working or heat treating the castings.

Another object of this invention is to convert high speed steels into adesired grain and carbide particle size for cutting tools without hotworking the metal.

Another object of this invention is to utilize an indirect are electricfurnace for producing a desired grain and carbide particle size in highspeed steel.

A further object of this invention is to improve the hardness andresistance to impact of cutting tools by heat treating the same attemperatures below their critical points.

Other and further objects of this invention will become apparent tothose skilled in the art from the following specific examplesillustrating the invention. It should be understood that the examplesare intended only to give specific data relating to processes alreadycarried out and are not intended to limit the invention.

Example 1 A high speed toolsteel alloy of the following analysis:

. Percent Tungsten 18 Chromium 4 Vanadium 1 Carbon 0.84 Iron Balance wasmelted in an indirect arc electric furnace and poured into cold graphitemolds of the approximate desired tool bit size at temperatures between2845" F. and 2950 F. The furnace used was a Detroit Electric FurnaceCompany rocking type indirect are electric furnace. The furnace waslined with magnesite, the melting atmosphere in the furnace wasnon-oxidizing and predominately reducing, and the melt was agitated by acontinuous and increasing rocking angle of the furnace. I

The casting was allowed to solidify and cool in the mold. The cooledcasting was then stripped from the mold and directly ground andsharpened to form a cutting tool bit.

The resulting tool bit was then tested under fatigue conditions todetermine its relative tool life as compared with standard commercialgrade cutting tool bits. For this purpose a shaft of annealed S. A. E.3140 steel was cut with the tool bit at a cutting speed of 166 feet perminute with a .0127 inch feed at a depth of .1000 inch. Under theseconditions, the cast tool bit lasted 21.10 minutes before failure. Noattempt was made to cool the tool bit during the cutting operation. I

A high speed steel tool bit of the identical analysis, but madeaccording to the known process of hot working the metal to produce atool bit of the exact shape as the cast cutting tool bit, only had atool life of 5.06 minutes under the same conditions to which the casttool bit was subjected.

Other commercial cutting tool bits now on the market were also subjectedto the same'cutting tests to determine their tool lives. A cutting toolbit known as Dreadnaught" and having the following analysis: 1

Per cent Carbon .80 Manganese .28 Chromium 2.75

Tungsten 16.13 Vanadium 1.03

. Iron Balance had a tool life of 6.90 minutes under the sameconditions.

A commercial tool bit now on the market known as Cyclops B-6 having thefollowing analysis:

Per cent Chromium .l. 4 Tungsten 18 Vanadium 1, Carbon 0.65 Iron Balancehad a tool life of 8.45 minutes under the same conditions.

Another commercial tool bit known as Blue Chip and having an analysis asfollows:

- Per cent Carbon .70 Manganese .25 Chromium 4.00 Tungsten 18.00Vanadium 1.00 Iron Balance had a tool life of 5.44 minutes under thesame conditions.

The above comparisons clearly show that a high speed steel melted in anindirect are electric furnace and directly cast into the desired toolshape has a longer tool life than tool steels made by the usual forgingoperations.

Example 2 A high speed steel alloy of the following analysis:

was melted in an indirect are electric furnace and cast in cold graphitemolds at temperatures.

between 2845 and 2950 F. The castings were allowed to cool in the molds,were then ground The tools;

The heat treated tools were tested under fatigue 6 conditions, todetermine their tool life by using them to cut a shaft of S. A. E. 3140normalized steel alloy at a speed of 126 feet per minute with a feed of.0127 inch and a cut depth of .1000 inch. The tool life in minutes underthese fatigue conditions was 16 minutes. A tool. of Cyclops B-6 toolsteel, when tested under the same conditions, only had a tool life of2.21 minutes.

The tool as originally cast had a. Rockwell hardness of 60.5. After theone hour heat treatment, the Rockwell hardness was increased to 68.5.

Example 3 A high speed tool steel having the same analysis as the steeldescribed in Example 2 was cast under the same conditions described inExample 2, subjected to a one hour draw at 1050 F. and was cooled incirculating air to room temperature. The resulting tool was then testedby cutting a heat treated shaft of Ford copper-silicon steel. Thecutting conditions were as follows:

Speed a. feet per minute- 99.7 Feed inch .0127 Depth of cut do .1000

The one hour draw at 1050 F. increased the Rockwell hardness of the toolfrom 60 to 68. The tool life under the test conditions indicated was9.55 minutes.

A cutting tool of Cyclops B-6 steel had a tool life under the sameconditions of 2.40 minutes.

Example 4 A square tool bit having the same analysis of the tool ofExample 2 was subjected to a. one hour draw at 1100 F. and was cooled incirculating air to room temperature. The tool was then tested under thesame conditions outlined in Example 3.

The Rockwell hardness of the tool was increased from 61 to 67 by a onehour draw at 1100 F. The tool life under the conditions indicated was10.48 minutes.

Example 5 A tool bit having the analysis of Example 2 was cast accordingto the same procedure of Example 2 and was heated for one hour at 1050F., cooled in circulating air to room temperature and reheated to 1150F.'f01' one hour. The reheated casting was then quenched in oil to roomtemperature.

The double draw heat treatment increased the Rockwell hardness of thetool from 61 to 68 and the tool had a life of 8.46 minutes under the,

conditions indicated in Example 3.

Example 6 I process of this invention results in cutting tools.

having several times as great a tool life as the heretofore known forgedcutting tools or othergrades of ferrous metal cutting tools now on themarket. The single or double draw heat treatments of this inventionincrease the Rockwell hardnesses of the cast tools but these heattreatments are'not necessary to produce high-grade cutting propertiessince, as indicated in Example 1, the unheat-treated cast tool of thisinvention has a much superior tool life than known commercial tools.However, the impact values and hardness of a tool steel, such as steelof the 18-4-1 group, when castfrom the furnace as described, werematerially increased by single or double draw heat treatments, bothtreatments being at temperatures below the critical temperature of thesteels.

By this means an improved cutting tool may be manufactured at a lowercost, it being unnecessary to heat, forge and reheat the tools to givethem necessary physical properties.

I am aware that numerous details of the process maybe varied through awide range without departing from the principles'of this invention,- andI, therefore, do not purpose limiting the patent granted hereonotherwise than necessitated by the prior art.

I claim as my invention:

1. The process of making cutting tools without forging or heat treatingthe tools above their critical point which comprises melting a highspeed steel in an indirect are electric furnace, agitating the melt,casting the molten steel into molds of the approximate tool size,allowing the castings to solidify in the molds, and grinding thecastings to tool shape.

2. The process of making cutting tool bits without forging or heattreating operations which comprises melting a ferrous high speed steelalloy containing 18% tungsten, 4% chromium, 1% vanadium in an indirectare electric furnace until it is sufficiently molten to be readilypoured, agitating the molten metal, casting the molten metal in molds ofthe approximate tool size, allowing the castings to solidify in themolds and grinding the castings to tool shape. 7

3. The process of making tool steel which comprises melting a high speedsteel having an iron content of from 15% to 85%, a carbon content offrom .6% to 2.0% and the balance consisting of at least one of themetals selected from the,

group comprising tungsten, molybdenum, chromium, vanadium and cobalt, inan indirect are electric furnace until the metal is sufficiently moltento be readily poured, agitating the molten metal, casting the moltenmetal into molds of the approximate desired tool size, allowing themetal to solidify in the molds and grinding the -casting the metal intocold molds of the approximate tool size, and grinding the castings tosize and shape for use as cutting tools.

5. The process of making cutting tools without hot working or hightemperature heat treatment which comprises melting a. high speed toolsteel charge in an indirect are electric furnace, said tool steel chargecomprising 18% tungsten, 4% chromium, 1% vanadium and the balance iron,rocking the furnace to agitate the melt, pouring the molten metal intomolds of the approximate tool size and shaping the castings without hotworking the metal to the tool size.

6. The process of making cutting tools from high speed steel alloyswithout forging or other metal working operations which comprisesheating a high speed steel alloy in an indirect arc electric furnace totemperatures between 2845 and 2950 F., agitating the metal, pouring themolten metal into molds of the approximate tool size, allowing the metalto solidify in the molds, heating the resulting castings to temperaturesabove 1000 F., but below the critical point of the steel, and coolingthe castings to room temperature.

7. The process of making cutting tools without forging or metal workingoperations which comprises melting a high speed steel alloy charge in anindirect arc electric furnace, agitating the melt, casting the moltenmetal into molds of the approximate tool size, allowing the metal tosolidify in the molds, heating the castings to temperatures from 1000 to1150 F. for about one hour. and cooling the castings to roomtemperature.

8. The process of making cutting tools without forging or heat treatingthe metal above its critical point which comprises melting a high speedsteel alloy charge in an indirect are electric furnace, pouring themolten metal into molds of the desired tool size, allowing the metal tosolidify in the molds, heating the castings to temperatures of about1050 to 1100 F. for one hour, cooling the castings in circulating air toroom temperature, reheating the cooled castings to temperatures of 1050to 1150 F. for about one hour and quenching the reheated castings toroom I, temperature.

9. The process of increasing the hardness, resistance to impactandcutting properties of a high speed tool steel containing 18% tungsten,4% chromium, 1% vanadium which comprises preparing a melt of the steelin an indirect arc rocking type electric furnace, rocking the furnace toagitate the melt, casting the molten steel into a mold of approximatetool size, allowing the casting to cool, and subjecting the cooledcasting to a combination low temperature heat treatment into a mold ofthe approximate tool size, allowing the casting to cool, and heating thecooled casting to 1050 F. for at least thirty minutes, quenching thecasting in circulating air, reheating the quenched casting to 1050'1'.for at least thirty minutes and quenching the casting inoil.

11. The process of making castings adapted for use in preparing highspeed tool bits without forging or other metal working operations whichcomprises heating a high speed tool steel in an indirect are electricfurnace to superheat temperaturesbetween 2845" F. and 2950 F., agitatingthe metal, pouring the' molten metal into molds to form castings of theapproximate tool bit size, heating the castings to temperatures above1000 F. but below the critical temperature of the steel, cooling theheated castings to room temperature, reheating the castings totemperatures above 1000 F. but below the critical temperature of thesteel and again cooling the castings to room temperature.

12. The process of making cast high speed steel tool bits withoutforging or heat treating above the critical temperature of the steelwhich comprises melting a high speed steel containing about 18%tungsten, 4% chromium and 1% vanadium with, the heat of an electric arc,agitating the molten steel, casting the molten steel into molds of theapproximate bit size, allowing the castings to solidify in the molds andgrinding the castings to tool bit shape.

13. A cast cutting tool comprising a high speed steel alloy castdirectly from an agitated electric arc furnace melt into approximatetool size, said tool having high Rockwell hardness and prolonged toollife.

14. A cast high speed steel tool bit containing to iron, 0.6 to 2.0%carbon. and the balance consisting of at least one alloy metal selectedfrom the group comprising tungsten, molybdenum, chromium, vanadium andcobalt, having a Rockwell hardness of from 60 to 68 and obtainable bycasting directly into tool size from a rocked indirect are electricfurnace melt.

15. A cast cutting tool comprising a high speed steel alloy containingabout 18% tungsten, 4% chromium, 1% vanadium, and the balancesubstantially iron cast directly from an agitated indirect are electricfurnace melt into molds of the approximate tool size and having aRockwell hardness over 60.

16. A cast tool steel having a Rockwell hardness of about 67 comprisinga high speed steel alloy containing 18% tungsten, 4% chromium, 1%vanadium and the balance substantially iron and obtainable by meltingthe steel alloy with an in-

